When a circuit board having a predetermined electrical circuit is connected electrically to another circuit board, they are, in general, electrically and mechanically connected by using a stacking connector. The stacking connector is disclosed, for example in Japanese Patent Kokai (Laid-Open) Publication No. 8(1996)-228059(A).
Further, a technique for electrically connecting circuit boards using an anisotropic conductive film (ACF) has been developed. Such a technique is disclosed, for example, in Japanese Patent Kokai (Laid-Open) Publication No. 5(1993)-174889(A) and Japanese Patent Kokai (Laid-Open) Publication No. 6(1994)-268345(A). Further, as shown in Japanese Patent Kokai (Laid-Open) Publication No. 6(1994)-120671(A), there is a technique which employs solder as a connection member between circuit boards so as to ensure mechanical and electrical connection therebetween.
As a connection member, a pressure welding electrical connector is disclosed in Japanese Patent Kokai (Laid-Open) Publication No. 2003-197289(A), and a terminal for surface mounting is disclosed in Japanese Patent Kokai (Laid-Open) Publication No. 6-111869(A).
Furthermore, as a dimension of an electronic equipment is recently smaller and thinner, miniaturization of a semiconductor chip and a finer pitch of electrodes are advanced. Not only a higher technique but also a higher cost is required for forming on a printed board many lands and wiring patterns which are adapted to each pad of a semiconductor chip having a small size and fine pitch. For this reason, a method for mounting a semiconductor chip on a mother board as a parent printed board through an intermediate board which is called an “interposer” has been recently employed widely. This method allows a semiconductor chip to be mounted on a board by an existing mounting technique. As the interposer, there are a ceramic interposer and a resin substrate interposer. The ceramic interposer is excellent in terms of thermal conduction, and the resin board interposer has an advantage in terms of cost. This interposer is also a kind of connection member for connecting a circuit board to another circuit board.
A technique for employing the interposer is disclosed, for example, in Japanese Patent Kokai (Laid-Open) Publication Nos. 2002-313984(A), 2003-110060, and 2003-100962. A board whose function is the same as that of the interposer is disclosed, for example, in Japanese Patent Kokai (Laid-Open) Publication Nos. 8(1996)-236654(A), 2000-36648(A) and 10(1998)-107398.
Furthermore, a three-dimensional mounting technique is developed for realizing higher density mounting, by using a module with a built-in component. This technique realizes higher density mounting by disposing an electronic component such as an active component (for example, a semiconductor device), and a passive component (for example, a capacitor) within a substrate.
This three-dimensional mounting provides, for example, a module with a built-in circuit component as shown in FIG. 67 (see Japanese Patent Kokai (Laid-Open) Publication No. 11(1999)-220262(A). A module with a built-in circuit component 2000 shown in FIG. 67 consists of a substrate 2001 formed by staking insulating substrates 2001a, 2001b and 2001c, wiring patterns 2002 (wiring layers) formed on a principal surface and an inside of the substrate 2001, and a circuit component 2003 located within the substrate 2001 and connected to the wiring patterns. The wiring patterns 2002 are electrically connected to a via hole conductor 2004. The insulating substrates 2001a, 2001b and 2001c are made of, for example, a mixture of an inorganic filler and a thermosetting resin.
As described above, various connection members have been used. The connection members, however, have a problem in that they cannot accommodate further miniaturization and a much finer pitch of a circuit board and component. This problem is described below.
When a stacking connector is used, it is necessary to secure a space on a circuit board where the stacking connector is to be disposed. This prevents miniaturization of an electronic device. Further, when the circuit board is a flexible printed board (for example, a polyimide board) and the stacking connector is attached to this flexible printed board, a thickness of an electronic device is difficult to be small because the stacking connector itself has a relatively large thickness. Further, Japanese Patent Kokai (Laid-Open) Publication No. 8(1996)-228059(A) exemplifies an embodiment wherein a stacking connector is attached to a rigid circuit board (for example, a conventional printed board). Attachment of a rigid stacking connector to a flexible circuit board itself is relatively complicated and decreases a throughput of a production process. In addition, there is a limit as to adaptation to a fine pitch which is achieved by a connection technique with use of a stacking connector.
On the other hand, a technique with use of an anisotropic conductive film (ACF), as disclosed in Japanese Patent Kokai (Laid-Open) Publication Nos. 5(1993)-174889(A) and 6(1994)-268345(A) more easily adapts to a fine pitch as compared with the technique with use of the stacking connector. The anisotropic conductive film, however, is unstable relative to a temperature cycle including a high temperature and a high humidity depending on a base material, which causes a concern for a decreased reliability. Further, since the anisotropic conductive film has a constitution wherein conductive particles are dispersed in a resin film, a number of the conductive particles should be increased in order to ensure good conductivity. If the number of the conductive particles, however, is too large, a problem as to electrical insulation is caused. As a pitch is finer on a circuit board or a component which is to be connected by the ACF (anisotropic conductive film), a good balance between electrical conductivity and insulation is more difficult to be obtained.
A connection member disclosed in Japanese Patent Kokai (Laid-Open) Publication No. 2003-197289(A) includes a foamed member as an element. For this reason, this member is poorly self-sustained and should be disposed in a positioning guide when it is used, which limits mounting sites of an electronic component and a circuit board, and therefore reduces practicability. A connection member disclosed in Japanese Patent Kokai (Laid-Open) Publication No. 6(1994)-111869(A) is used as a surface mount terminal and therefore its shape and usage pattern are very limited. Further, Japanese Patent Kokai (Laid-Open) Publication Nos. 2003-197289(A) and 6(1994)-111869(A) do not teach a connection member for connecting an electronic component itself to a circuit board.
Furthermore, a prior art interposer has a problem described below. In a conventional interposer, electrical conduction between an upper surface and a lower surface is ensured by a via which is filled with a conductor. Therefore, it is necessary to form the via upon producing the interposer. Formation of the via needs a paste-filling step or a plating step in addition to a boring step for forming a through hole, which involves complications. Further, from a viewpoint of production cost, more resin interposers have been used instead of ceramic interposers. Since miniaturization of a semiconductor device gives rise to increase in calorific value, thermal conductivity of the resin interposers is essentially required to be increased.
Further, a connection structure with a solder ball is generally employed in a technique for mounting a semiconductor chip on a mother board as a parent printed board with a conventional interposer. The connection structure with a solder ball is limited by ball size and a connection pitch is larger as the solder ball is larger, which provides a limitation on narrowing pitch. Particularly, with a mounting structure wherein an interposer strides and covers a tall component, it is necessary to use a solder ball having a size corresponding to a height of the component, which results in a very large connection pitch. Further, since there is fluctuation in a size of a solder ball, a solder ball connection may not be made at some positions. Thus, the solder ball connection may be unstable, which reduces a product yield in a worst case. Furthermore, connection with use of a solder ball requires mounting solder balls one by one, and therefore has a problem of low productivity.
On the other hand, a built-in component technique has been developed as a three-dimensional mounting technique as described above. However, in this technique, a built-in component cannot be easily repaired or exchanged and additional cost is required to introduce a special instrument for three-dimensional mounting, which might be an obstacle to practical use of this technique.
The present invention is made in light of the problems of the conventional connection member, and an object of the present invention is to provide a connection member which has a construction different from that of a conventional one, so that it accommodates to fine pitch and it can be produced relatively efficiently, and to provide a method for producing the connection member. Another object of the present invention is to provide a module and a mount assembly which are obtained using the connection member.